1. Field of the Invention.
This invention relates generally to migratory fish in rivers and streams. More particularly, this invention relates to fish ladder apparati for assisting migratory fish in overcoming river and stream obstructions such as dams, especially in the upstream direction.
2. Related Art.
Many devices have been designed and built to assist fish in overcoming dams. Often, these devices have been culverts, flumes or sluices with internal baffles. Typically, the culvert is tipped at an angle to match the upward grade change in the waterway, and water flows down through the culvert. The baffles may have vertical slots or lowered horizontal weir edges for permitting passage of the fish up through the water in the culvert. The migrating fish may take short rests on the upstream side of the baffles and weir edges.
Otherwise, these migratory fish assistance devices have been angled ramps with bristles, for example, installed on the top surface of the ramp. Otherwise, these devices have also been mechanically powered elevators, lifts or locks which allow the fish to be transported over the dam. See, for example, Innovations in Fish Passage Technology, edited by Mufeed Odeh (Published by The American Fisheries Society, Bethesda, Md.xe2x80x941999).
U.S. Pat. No. 1,573,785 (Albright) discloses a water-wheel-driven fish ladder with a belt conveyor for lifting fish over a dam.
U.S. Pat. No. 4,260,286 (Buchanan) discloses a fish ladder comprising an edge-to-edge length-wise series of ascending dish-like compartments. The dish-like compartments are arranged end edge to end edge from the bottom to the top of the ladder, and water overflows from the top to the bottom of the ladder. Auxiliary water input may be provided to each dish in the series to maintain the desired turbulence in each dish and flush debris from the ladder.
U.S. Pat. No. 5,139,364 (Takahashi, et al.) discloses an inclined ramp fishway with internal weir/baffles. The ramp is pivotable vertically to accommodate different water levels at the upstream end of the ramp.
Still, there is a need for a compact, easy-to-build fish ladder for assisting fish in easily and safely overcoming dams, especially in the upstream direction. This invention addresses that need.
The present invention is a safe and effective fish ladder for assisting fish in overcoming dams, especially in the upstream direction. The ladder comprises a series of open pools, which decrease in size in the upstream direction, the pools being conveniently spaced apart a vertical distance which may be easily jumped by the particular fish species of interest. By being arranged relatively vertically, so that the downstream perimeter of one pool is substantially within the downstream perimeter of the pool directly beneath the one pool, the fish ladder does not need to be long and expensive if the dam to overcome is high. Also, by being relatively vertical, the ladder may be conveniently built onto already existing vertical structures on the downstream side of a dam, for example, onto the support structure for the discharge flume for downstream migrating fish in the apparatus disclosed in U.S. Pat. No. 5,161,913 (Boylan), incorporated herein by reference. Or, the ladder of the present invention may be built even onto the downstream side of the dam itself. Preferably, the fish ladder of the present invention is made of a smooth material which does not aggravate the sensitive skin of the fish.